Process for the hydrometallurgical treatment of a solution of materials containing gallium

ABSTRACT

A process of hydrometallurgical treatment of a solution of materials containing gallium and at least one metalloid from Group V of the periodic table of the elements which comprises adding hydrochloric acid and an alkali metal chloride or an alkaline earth metal chloride to said solution to form gallium chloride so that the concentration of chloride ions, not counting those bonded to gallium, is in a range of from 4 to 10 N and the acidity of said solution is in a range of from 1 to about 5 N. Then placing the adjusted solution in contact with an organic phase comprising at least one neutral pentavalent phosphorus compound having a phosphorus-oxygen double bond, wherein the gallium chloride is extracted by the organic phase and reextracting the gallium from the organic phase.

The present invention relates to the recovery of gallium contained invarious raw materials or secondary raw materials together withimpurities such as the metalloids of Group V of the periodic table ofthe elements.

More particularly it relates to the treatment either of solutions ofgallium chloride, or of materials containing gallium in the wholly orpartially reduced state.

As an example of reduced materials of this kind containing gallium maybe mentioned gallium metal and the phosphides, arsenides, nitrides andantimonides of this metal.

Gallium, whether present in primary or secondary raw materials, is oftencombined with Group V elements: thus, the dust from phosphorus plants,the residues from processing of gallium arsenide and gallium phosphideand so on.

For economic reasons, it is preferable that the processes for thetreatment of these products or of these solutions employ techniques ofthe chloride route already partially perfected for the primary recoveryof gallium where impurities of this kind do not occur. In general thesetechniques employ trialkyl phosphates, particularly the most common ofthese tributyl phosphate, currently designated by its letter symbol inEnglish TBP, which will serve as a paradigm for this family (cf. Scienceand Technology of tributyl phosphate, volume 2, pages 97-99, RC PressInc).

An initial difficulty lies in the presence, among the materialscontaining gallium, of other elements having similar chemical propertiessuch as, for example, indium and more generally metals having volatilesuboxides. Furthermore, the Group V elements often have propertiessimilar to those of III compounds, which makes separation difficult.

According to the conventional techniques for the recovery of gallium,this element is brought into hydrochloric acid solution and is recoveredby liquid-liquid extraction of the gallium trichloride formed by meansof liposoluble complexing agents of Lewis acids, agents such as aminesand neutral organophosphorus compounds of the trioctylphosphine oxide(TOPO) and tributyl phosphate (TBP) type.

A second difficulty in the treatment of these secondary raw materialslies in the particularly pyrophoric and inflammable nature of theseproducts and of the gases which they produce from their reaction withwater. Thus in aqueous phases gallium phosphide produces phosphines,compounds which are very inflammable, certain of which would be thesource of the combustion of natural evolutions of methane and wouldcause what is commonly called "will-o'-the-wisps".

It is also advisable to mention that the hydrogenous compounds ofarsenic, antimony and phosphorus are highly toxic.

One of the objects of the present invention is to provide a processderived from the processes above but adapted to the particular problemsof materials containing gallium mentioned above.

Thus, one of the objects of the present invention is to provide aprocess which enables, starting from the same extractive reactants aspreviously used, a good separation of gallium in the form of thechloride to be ensured from the Group V metalloids or from theimpurities which are likely to be present in wastes of gallium III-Vcompounds or in other sources of supply of materials containing gallium.Among these impurities may be mentioned indium and antimony.

These objects as well as others which will appear subsequently areachieved by means of a process of hydrometallurgical treatment of asolution of materials containing gallium comprising in addition at leastone metalloid from Group V of the periodic table of the elements,characterized in that it comprises the following steps:

b) adjustment of the concentration of chloride ions and the acidity ofthe solution to be extracted (for example obtained from step a)described below by addition of hydrochloric acid and an alkali metalchloride or an alkaline earth metal chloride;

c) placing the said solution in contact with an organic phase comprisingat least one neutral pentavalent phosphorus compound having aphosphorus-oxygen double bond.

Once the gallium placed in solution at a concentration preferably atleast equal to 20 g/l, advantageously from 30 to 200 g/l (the zeros notbeing significant figures), it is advisable to make it suitable forextraction by neutral pentavalent phosphorus compounds by controllingthe level of acidity and the concentration of chloride ions so that thelatter reaches a value in the range 4 to 10N, while the level of aciditymust be greater than 1N, preferably greater than 3N, advantageouslyabout 5N.

The liquid-liquid extraction, after this adjustment, is preferablycarried out with phosphorus compounds of the above type which arecommercially available, such as TOPO or preferably the most commontrialkylphosphate, that designated by the English acronym TBP English(tributylphosphate).

With the aim of better controlling the liquid-liquid extraction, bothwith regard to the level of viscosity and to the chemical properties, itis desirable that the trialkyl phosphate should be dissolved in aromatichydrocarbons; in general petroleum fractions having a high boiling pointand a high ignition point, such as those of the type sold under thetrademark Solvesso 150, are used as aromatic hydrocarbons. Generally,for economic reasons, tributyl phosphate, better known under its Englishacronym TBP, is used as trialkyl phosphate.

The organic phase preferably contains from 20 to 60%, advantageouslyfrom 30 to 50% of trialkylphosphate by volume.

In order to be selective with regard to the impurities mentioned above,it is advisable to carry out the liquid-liquid extraction in such a waythat the concentration of gallium chloride in the organic phase is atleast equal to 90%, preferably to 95%, advantageously to 99% of itssaturation value if it were the only extractable element.

In order to do this, adjustment is made essentially to the ratio of theorganic phase to the aqueous phase limiting it as much as possible. As aguide, it will be possible to adjust the quantity of phosphoruscompounds used per unit of gallium present in the solution (control ofoutputs). A ratio of two molecules of organophosphorus compounds permolecule of gallium chloride must be sought. It is thus preferable to beoperating in the section of the extraction isotherm where this curveforms a quasi plateau. This is achieved particularly by adjusting theprescribed level of chloride and the prescribed level of acidity in stepb). Thus, the ratio of the saturation value to the actual extractionvalue must be as close as possible to 1, hence the importance ofobtaining very high gallium concentrations and, indeed, from step a)described below, equally high solids contents of the suspension,preferably in the range 50 to 500 grams per liter (to one significantfigure).

Finally, to be more selective with regard to arsenic, the latter beingless well extracted by the phosphorus compounds in the V form than inthe III form, it is advantageous that an oxidation is carried out insuch a way that at least two thirds, preferably 95%, advantageously 99%of the arsenic is present in the pentavalent form. This oxidation can becarried out at the time of the possible step a) below. This ratio,following Nernst's Law determines the redox potential of the solution. Asatisfactory potential is a potential which is in the region of 1 V withreference to the Ag/AgCl electrode.

When the organic phase contains some other impurity, it is possible towash this phase with solutions of concentrated gallium chloride. One ofthe best possibilities is to wash the said organic phase with anHCl-CaCl₂ mixture at the highest possible O/A ratio. The galliumchloride thus obtained can advantageously be recycled for example in theaqueous suspension phase of the possible step a) below.

The number of extraction stages is determined so that the extraction ofgallium should be as complete as possible with as low as possible aconcentration of impurities at the outlet. The number of stages isgenerally within the range 3 to 5.

Another object of the present invention is to provide a leaching processfor compounds containing gallium mentioned above which gives galliumchloride and which avoids or limits the formation of toxic orinflammable gases.

Another aim of the present invention is to provide an aggressive processwhich avoids any untimely ignition of these materials containinggallium.

It is noteworthy that avoidance of ignition of these materialscontaining gallium or the gases which they generate is particularlyimportant when these materials containing gallium comprise in additionorganic diluents such as those used during processing of III-Vcompounds.

This object is achieved by means of the addition, before step b) of thefollowing step: a) placing gallium in solution by attacking a suspensionof the said materials containing gallium with chloride;

Attacking compounds of this type with chlorine is known per se but it isparticularly difficult to carry out in aqueous media. It is for thisreason that in a recent patent application (European Patent Applicationpublished under No. 0,219,213 filed by the company SUMITOMO METALMINING), it has been proposed to attack compounds of this type in a bathof molten salts whose principal constituent is arsenic chloride. Thishas led to carrying out the separation of the arsenic chloride fromgallium chloride by distillation, despite the difficulty of a techniqueof this type.

In general, when chlorine is used in the aqueous phase to attackcompounds of this type there is a high risk of explosion andparticularly expensive equipment is necessary to avoid the risks of fireas well as poisoning.

During the study which led to the present invention it was possible todemonstrate that operating in regions, at least at the start of thereaction, where it is not usual to operate for dissolving gallium, thatis at a pH where chloride is not present in solution(disproportionation>about 3) and where gallium is normally insoluble asit is precipitated in the form of the trihydroxide, it was possible toavoid any ignition and any evolution of toxic materials.

It is preferable that the temperature of the solution during theaggressive step a) should be less than 80° C., advantageously at mostequal to 50° C. (these two latter values are given to a singlesignificant figure).

When chlorine is mentioned, it must be understood to mean not onlygaseous chlorine but also any operation capable of generating chlorine"in situ". As examples of the evolution of chlorine "in situ" may bementioned electrolysis in a chloride medium and reactions opposite tothat of the disproportionation of this halogen.

One of the possible embodiments of the present invention would compriseintroducing chlorine in the form of hydrochloric acid and bleachingpowder (mixed chloride and hypochlorite of lime one of the proposedformulae of which is CaClOCl), with the provision that the aciditylimits specified above are followed.

One of the satisfactory ways of carrying out the reaction comprisesstarting with an aqueous phase having a pH within the range above(absence of dissolved chlorine and presence of precipitates of galliumhydroxide), namely a pH within the range 3 to 8, forming a pulp with theproduct containing gallium (step a) and bubbling chlorine gas throughit, then the temperature is allowed to rise under the effect of thereaction exotherm.

After step c), it is possible to carry out, according to techniquesknown to practitioners of the art, a rinsing of the organic phase toeliminate particles of the aqueous phase which have been entrained inthe organic phase. A washing of this type occurs in Example 4.

Step c) of liquid-liquid extraction can be followed, as far as theaqueous phase is concerned by a step of recovery or elimination ofarsenic. These steps are known per se. As recovery step, may bementioned a reduction of arsenic V to arsenic III followed by adistillation known per se of the arsenic trichlorides. From theenvironmental aspects, it is also possible to precipitate the arsenic inthe form of arsenate of lime and iron arsenate by adding one of thesetwo elements in an appropriate form and adjusting the pH to the pH fromprecipitation of the arsenate of lime and the iron arsenate. Thechloride solutions thus obtained can possibly be the subject ofrecycling to step a) or, after evaporation and salt formation, to stepb).

The organic phase loaded with gallium chloride, possibly washed asdescribed above, can be eluted in a step d) either by an aqueous phasewhich is lean in chloride ions (less than 1N, preferably less than0.1N), or preferably reextracted by a medium containing sodium ions toform on the one hand a gallate of sodium or of another alkali metal andon the other hand sodium chloride or the chloride of another alkalimetal.

This solution allows complete regeneration of TBP and allows in additiona step e) for recovery of gallium by electrolysis.

For this electrolysis step e), it is preferable that the concentrationof free base (OH⁻) is greater than 4N. It is thus possible to carry outstep d) of sodium carbonate elution, either by placing in contact withsodium carbonate at a quantity and in a concentration such that theresidual sodium carbonate is at least equal to 0.1N, preferably equal to0.5N, and subsequently adjusting the quantity of base, or by placing theTBP solution in contact with a base in a quantity and a concentrationsuch that, after the reextraction, the quantity of residual base is atleast equal to 4N.

Thus the electrolysis step is preferably carried out with a sodiumcarbonate concentration at least equal to about 4N at current densitieswithin the range 80 (to one significant figure) and 300 (to onesignificant figure) A/m² and at a temperature in the range 35° to 50° C.

The examples which follow and which do not introduce any limitingcharacteristic are intended to enable specialists to determine readilythe operating conditions which it is advisable to use in each particularcase.

EXAMPLE 1

100 g of gallium arsenide process sludges containing 45.5% of galliumand 47.9% of arsenic are placed in suspension in 500 ml of water. Noarsine (AsH₃) is detected above the reaction vessel and no violentreaction is produced. Chlorine gas is subsequently injected into thestirred suspension at the rate of 80 g/h for 7 hours, during which thetemperature rises to 75° C.

Once the attack is finished, the suspension is filtered, the residue iswashed with water and 4.46 g of dry residue is recovered containing19.4% of gallium and 0.60 l of aqueous solution containing galliumchloride. The lixiviation yield of gallium is thus greater than 98%.

EXAMPLE 2

100 g of gallium phosphide process sludges, containing 56.5% of galliumand 18.5% of phosphorus, are placed in suspension in 500 ml of water. Notrace of phosphines (PH₃, P₂ H₄, and so on) is detected above thereaction vessel and no ignition is produced. Chlorine gas issubsequently injected into the stirred suspension at the rate of 100 g/hfor 7 hours. The temperature of the suspension rises to 76° C. duringthe reaction. When the attack is finished, the suspension is filtered,the residue is washed with water and 12.5 g of dry residue is recoveredcontaining 0.76% of gallium and 600 ml of solution containing galliumchloride.

The lixiviation yield of gallium is thus greater than 99%.

EXAMPLE 3

100 g of broken gallium phosphide wafers, previously pulverized to agranulometry of d₈₀ =240 μm, containing 71.1% of gallium and 25.7% ofphosphorus are placed in suspension in 500 ml of water. No trace ofphosphine (PH₃) is detected above the reaction vessel and no ignition isproduced. Chlorine gas is subsequently injected into the stirredsuspension at the rate of 100 g/h for 7 hours. The temperature of thesuspension rises to 76° C. during the reaction. When the attack isfinished, the suspension is filtered, the residue is washed with waterand 0.97 g of dry residue is recovered containing 33.4% of gallium and620 ml of solution containing gallium chloride.

The dissolution yield of gallium is thus greater than 99%.

EXAMPLE 4

By placing gallium in solution by using chlorine to attack a suspensionof materials containing gallium defined in Examples 1, 2 and 3, andafter addition of CaCl₂, a solution PHA_(infl) is obtained whosepotential relative to the Ag/AgCl electrode is about one volt and whichis placed in contact, under countercurrent conditions in a battery of 4mixer-settlers, with an organic phase formed by volume from 40% TBP and60% SOLVESSO 150, while maintaining a ratio of organic phase to aqueousphase (O/A) of 0.9; after allowing the battery to reach chemicalequilibrium, an organic phase PHO_(eff) is obtained whose composition,like that of PHA_(infl), is given in the table below.

In a second stage, this organic phase loaded with gallium is placed incontact with an aqueous phase titrating HCl=1N and CaCl₂ =2M, so as toobtain an O/A ratio of 10, under countercurrent conditions in a batteryof 4 mixer-settlers. The organic phase is thus completely purified andafter allowing the battery to reach chemical equilibrium an organicphase PHO_(lav) and an aqueous washing phase PHA_(lav) are obtainedwhose respective compositions are given in the table below.

    ______________________________________                                        Chemical PHASES                                                               Species  PHA.sub.infl                                                                           PHA.sub.eff                                                                           PHO.sub.eff                                                                           PHO.sub.lav                                                                          PHA.sub.lav                          ______________________________________                                        Ga in g/l                                                                              46.1     0.2     51.1    46.2   49.2                                 As in g/l                                                                              23.6     23.4      0.164 5.10.sup.-3                                                                          1.6                                  In in g/l                                                                              0.46     0.45    10 × 10.sup.-3                                                                   <10.sup.-3                                                                          0.1                                  P in g/l 8.7      8.6                                                         CaCl.sub.2 in M                                                                        1.5      1.5                    2                                    HCl in N 5        2.7                    2                                    Selectivity of re-                                                            covery of gallium                                                             in relation to:                                                               arsenic           160        29                                               indium             51        <9                                               Cumulative selectivity:                                                       arsenic                     4640                                              indium                      <460                                              ______________________________________                                    

EXAMPLE 5

A solution of gallium chloride in TBP (40%) obtained by placing thelatter under the conditions of the invention in contact with anindustrial solution of gallium chloride is twice placed in contact with2N sodium carbonate at a ratio O/A=1. The results are compiled in thetable below.

The sodium carbonate consumed is equal to 1.85N.

    ______________________________________                                        Vol-                                                                          ume        Ga      As     In   Na   Cl.sup.-                                                                           Ca   OH.sup.-                        (1)        g/l     mg/l   mg/l g/l  g/l  mg/l (N)                             ______________________________________                                        Initial  4.15  37.7    44   2    --   --   --   --                            Organic                                                                       phase                                                                         Organic --     0.025   21   1    --   --   --   --                            phase                                                                         1st contact                                                                   Aqueous 4.4    32.5    12   1.6  30.0 61.4 15.9 0.85                          phase                                                                         1st contact                                                                   Organic 4.1    0.021   17   1    --   --   --   --                            phase                                                                         2nd contact                                                                   Aqueous 4.3    3.2     16   2.5  19.1 35.8 35.8 1.3                           phase                                                                         2nd contact                                                                   Re.extrac-     99.9    62.0 50.0                                              tion                                                                          yield %                                                                       ______________________________________                                    

EXAMPLE 6

Electrolysis of gallium obtained in solutions from reextraction withsodium carbonate.

Electrolysis trials were carried out starting from sodium carbonatereextraction solutions and varying as parameters the concentration offree sodium carbonate and the current density using thermal control tokeep the catholyte and the anolyte at 40° C. The cathodes and anodes areof stainless steel and a recovery boat for liquid gallium is located atthe lower end of the cathode. During the electrolysis, the drops ofgallium flow along the surface of the cathode (vertical) and arecollected in the said boat. The solution containing gallium whichsupplies the electrolysis tank has the following composition:

Ga=32.5 g/l

Cl⁻ =61.4 g/l

Na=30.0 g/l

OH⁻ =0.85N

As=12 mg/l

In=1.6 mg/l

The parameters for the different trials are compiled in the followingtable:

    ______________________________________                                             Initial  Current  Dura- Faradic                                          OH.sup.-                                                                           concen-  density  tion  yield  Anodic                                    (N)  tration  A/m.sup.2                                                                              (h)   %      phenomena                                 ______________________________________                                        0.85 32.5     250      12    60 to 14                                                                             Evolution of Cl.sub.2,                                                        formation of                                                                  hypochlorites,                                                                attack                                    0.85 32.5      80      3     62     Evolution of Cl.sub.2,                                                        attack                                    2    25        80      3.5   83     No dissolution                                                                appearance of                                                                 some pitting                              2    25       120      5     79     Slight attack                             3    20       120      4.5   77     No attack, anolyte                                                            colourless                                3    15       240      2.5   72     No attack anolyte                                                             slightly yellow                           ______________________________________                                    

The gallium obtained has a purity greater than 99.99% (In and As underthe limit of detection, that is less than 3 g/t and less than 8 g/trespectively).

EXAMPLE 7

A solution of gallium chloride in TBP (loaded organic phase obtained byplacing the latter under the conditions of the invention in contact withan industrial solution of gallium chloride is placed in contact,continuously within a stirred reaction vessel, with 7N sodium hydroxydeat a ratio O/A=1.4. The gallium in the sodium carbonate afterreextraction is analysed. The sodium carbonate consumed is equal to2.6N. The results are compiled in the following table:

    ______________________________________                                        Phases                                                                                 Loaded    Sodium carbon-                                                                             Sodium carbon-                                Chemical organic   ate before   ate after                                     Species  phase     reextraction reextraction                                  ______________________________________                                        Ga in g/l                                                                              45.0                   64.0                                          As in mg/l                                                                             15 × 10.sup.-3   0.02                                          In in g/l                                                                              <10.sup.-3                                                           NaOH in N          7                                                          ______________________________________                                    

The reextraction yield of gallium is greater than 99.9%.

I claim:
 1. A process of hydrometallurgical treatment of a solution ofmaterials containing gallium and at least one metalloid from Group V ofthe periodic table of the elements, comprising the steps of:a) addinghydrochloric acid and an alkali metal chloride or an alkaline earthmetal chloride to said solution to form gallium chloride so that theconcentration of chloride ions, not counting those bonded to gallium, isin a range of from 4 to 10N and the acidity of said solution is in arange of from 1 to about 5N; b) placing the adjusted solution of step a)in contact with an organic phase comprising at least one neutralpentavalent phosphorus compound having a phosphorus-oxygen double bond,wherein the gallium chloride is extracted by the organic phase; and c)reextracting the gallium from the organic phase.
 2. Process according toclaim 1, wherein said phosphorus compound is a trialkylphosphate. 3.Process according to claim 2, wherein said phosphorus compound istributylphosphate.
 4. Process according to claim 1, wherein step b iscarried out so that the concentration of gallium chloride in the organicphase is equal to 90% of its saturation value if it were the onlyextractable element.
 5. Process according to claim 4, the control of theconcentration of gallium chloride is carried out through the ratio oforganic phase to aqueous phase.
 6. Process according to claim 1, whereinthe redox potential of the solution before step a is such that twothirds of said at least one metalloid from Group V of the periodic tableof the elements is in the pentavalent form.
 7. Process according toclaim 1,wherein the reextraction step of gallium from said organic phasetakes place in a sodium hydroxide medium.
 8. A process according toclaim 1, further comprising the step of d) recovering the reextractedgallium by electrolysis in an electrolyte whose concentration of freebase is at least equal to 4N.
 9. A process of hydrometallurgicaltreatment of a solution of materials containing gallium and at least onemetalloid from Group V of the periodic table of elements, comprising thesteps of:forming a suspension from an aqueous composition comprisinggallium and at least one metalloid from Group V of the periodic table byadjusting the pH thereof to a value not lower than 3, so that thegallium forms an insoluble trihydroxide; blowing chlorine gas throughthe thus-obtained suspension; separating solids therefrom to obtain asolution; adding hydrochloric acid and an alkali metal chloride or analkaline earth metal chloride to said solution to form gallium chlorideso that the concentration of chloride ions, not counting those bonded togallium, is in a range of from 4 to 10N and the acidity of said solutionis in a range of from 1 to about 5N; placing the adjusted solution ofthe immediately preceding steps in contact with an organic phasecomprising at least one neutral pentavalent phosphorus compound having aphosphorus-oxygen double bond, and extracting the gallium chloride bythe organic phase; and reextracting the gallium from the organic phase.10. Process according to claim 9, wherein the temperature of saidsolution during step a1) is in a range of from about 50° to about 70° C.11. Process according to claim 9, wherein said suspension of saidmaterials containing gallium is an aqueous suspension produced atambient temperature.
 12. Process according to claim 11, wherein duringstep a1) the temperature is allowed to rise under the effect of thereaction exotherm.
 13. Process according to claim 11, wherein at thebeginning of step a1) said solution has a pH within the range from 3 to8.
 14. Process according to claim 9, wherein the concentration of solidsin the suspension of materials containing gallium is in the range 50 to500 grams per liter.